"The problem than arises of when to define operationally the duration of bullying behaviours. Leymann (1990b, 19960=) suggested exposure for more than six months as an operational definition of bullying at work. Others have used repeated exposure to negative behaviours within a six-month period as the proposed timeframe (Einarsen and Skogstad, 1996). Leymann's strict criterion has been argued to be somewhat arbitrary, as bullying seems to exist on a continuum from occasional exposure to negative behaviours to severe victimisation resulting from frequent and long-lasting exposure to negative behaviours at work (Mattiesen et al., 1989). Yet, the criterion of about six months has been used in many studies in order to differentiate between exposure to social stress at work and victimisation from bullying (e.g. Einarsen and Skogstad, 1996; Mikkelsen and Einarsen, 2001; Niedl, 1995; Varita, 1996; Zapf et al. 1996). The reason for this criterion for Leymann (1993, 1996) was to argue that mobbing leads to severe psychiatric and psychosomatic impairment, stress effects which would not be expected to occur as a result of the normal occupational stressors such as time-pressure, role-conflicts or everyday social stressors. Hence, the period of 6 months was chosen by Leymann because it is frequently used in the assessment of various psychiatric disorders."